The attacks were first spotted by the security firm FireEye, which identified the target as VFW.org, the homepage of the Veterans of Foreign Wars. "We believe the attack is a strategic Web compromise targeting American military personnel amid a paralyzing snowstorm at the US Capitol in the days leading up to the Presidents Day holiday weekend," reps for FireEye wrote on the company blog.

FireEye believes that hackers used a vulnerability in Internet Explorer 10 to "silently redirect" visitors from VFW.org to a shadow site, in the process infecting thousands of computers with spyware. (You can find a more thorough explanation of the zero-day attack here, courtesy of the FireEye team, but unless you're a computer professional, you'll want to have easy access to a dictionary of technical terms.)

"We are investigating and we will take appropriate actions to help protect customers," the company said in a statement.

But that may not be the end of the threat. In an interview with Computerworld, Darien Kindlund, manager of threat intelligence for FireEye, said the perpetrators of the attack – dubbed "Operation SnowMan" by FireEye – were committed and likely "fairly sophisticated."